1. Field of the Invention
The present invention relates to an optical scanning system of a printer and a driving method thereof and, more particularly, to an optical scanning system of a printer which can prevent a writing error of line image data on a photoreceptor web due to the difference in the amount of light reflected by each of the mirror surfaces of a polygonal rotating mirror, and a driving method thereof.
2. Description of the Related Art
FIG. 1 shows an optical scanning system of a conventional printer. Referring to the drawing, an optical scanning system includes an optical scanning unit 20 for scanning light onto a photoreceptor web 14 circulating by being supported by a plurality of rollers 11, 12 and 13, a photodetector 26, a line scanning start determination portion 31 and an optical scanning controller 32.
The optical scanning unit 20 includes a light source 21, a polygonal rotating mirror 22, a lens unit 23, and a driving source 24. The polygonal rotating mirror 22 is rotated at a predetermined speed by the driving source 24. The photodetector 26 is installed to detect light emitted from the optical scanning unit 20 and scanned from a position off the photoreceptor web 14 to the edge of the photoreceptor web 14.
The line scanning start determination portion 31 outputs a line scanning start signal after a predetermined wait time with respect to a light receiving termination point of a pulse signal output by the photodetector 26 corresponding to light reception. The wait time corresponds to the time needed to scan light in a non-image zone N from the edge of the photoreceptor web 14 to the image writing zone D. The optical scanning controller or controlling portion 32 drives the light source 21 so that light corresponding to line image data is emitted in synchronization with the line scanning start signal.
However, in the conventional optical scanning system, the respective mirror surfaces, such as mirror surfaces 22a and 22b, of the polygonal rotating mirror 22 reflect different amounts of light due to a manufacturing error. That is, FIG. 2 shows an example of the pulse signal output from the photodetector 26, when the respective mirror surfaces 22a and 22b of the polygonal rotating mirror 22 are assigned their own numbers and the amount of light reflected from the mirror surfaces 22a and 22b are different. The line scanning start determining portion 31 compares the pulse signal output from the photodetector 26 with a predetermined reference level signal and determines and processes an input signal over a reference level set to restrict a signal processing error due to noise, as a light receiving pulse signal. As a result, according to a line scanning synchronizing method for each mirror surface by the conventional optical scanning system, the line image data writing start position is different on the photoreceptor web 14, as much as the pulse width difference d between the light receiving termination positions of the pulse signals corresponding to the mirror surfaces 22a and 22b with respect to the set reference level. Thus, the writing start position of the image data for each line written on the photoreceptor web 14 is uneven along the circulating direction of the photoreceptor web 14, with a period of the number of lines which corresponds to the total number of the mirror surfaces of the polygonal rotating mirror 22.
To solve the above problem, it is an object of the present invention to provide an optical scanning system of a printer which can write image data for each line on a photoreceptor web with the writing start positions of each line perfectly aligned by correcting the difference in the amount of light reflected from each mirror surface of a polygonal rotating mirror, and a driving method thereof.
Accordingly, to achieve the above object, there is provided an optical scanning system of a printer, which comprises an optical scanning unit including a light source, a rotating polygonal mirror having a plurality of mirror surfaces for deflecting light emitted from the light source toward a photoreceptor web, and a driving source for driving the rotating polygonal, mirror. The optical scanning system further comprises a photodetector installed to receive light scanned by the optical scanning unit to a position off the photoreceptor, and a controller for controlling a scanning start point of image data for lines by the optical scanning unit by obtaining information on addresses of mirror surfaces of the rotating polygonal mirror while counting the number of pulse signals output from the photodetector corresponding to the light received thereby, and by applying a line scanning synchronization correction time corresponding to the mirror surface address information with respect to a light receiving termination point of the pulse signal, to correct a line scanning synchronization time according to the difference in the amount of light reflected from each mirror surface of the rotating polygonal mirror.
It is preferable in the present invention that the controller comprises a pulse counter for counting the number of pulse signals output from the photodetector and outputting a count value, a scanning synchronization correction time calculation portion for mirror surfaces for obtaining information on addresses of mirror surfaces of the rotating polygonal mirror from the count value output from the pulse counter, and calculating the correction time corresponding to the surface mirror address information from the amount of change in width of the pulse signal output from the photodetector, a line scanning start determination portion for outputting a line scanning start signal when it has received the correction time output from the scanning synchronization correction time calculation portion with respect to the light receiving termination point of the pulse signal output from the photodetector, and an optical scanning controlling portion for controlling the light source so that light corresponding to the line image data is emitted in synchronization with the line scanning start signal.
Also, it is preferable in the present invention that the scanning synchronization correction time calculation portion for each line calculates a correction time corresponding to the mirror surface address information and stores the calculated time when a correction time calculation instruction signal is received from the optical scanning controlling portion, and outputs the stored correction time to the line scanning start determination portion corresponding to the count value output from the pulse counter when a printing mode signal is received from the optical scanning controlling portion.
To achieve the above object, there is provided a method of driving an optical scanning system of a printer, the optical scanning system including an optical scanning unit having a light source, b) a rotating polygonal mirror having a plurality of mirror surfaces for deflecting light emitted from the light source toward a photoreceptor web, and c) a driving source for driving the rotating polygonal mirror, 2) a photodetector installed to receive light scanned by the optical scanning unit to a position off the photoreceptor, and 3) a controller which controls a line scanning start point of image data for lines by the optical scanning unit by receiving a pulse signal output corresponding to light received by the photodetector and which corrects the difference in the amount of light reflected from each mirror surface of the rotating polygonal mirror.The method is achieved by stopping the photoreceptor web, counting the number of pulse signals output from the photodetector while the optical scanning unit scans light, and calculating a scanning synchronization correction time for lines with respect to the difference in the amount of light reflected from each mirror surface, and storing the calculated is result by calculating the difference in width between the pulse signals with respect to addresses of the mirror surfaces of the rotating polygonal mirror corresponding to the count value, and when there is a request for printing while continuously counting the number of pulse signals output from the photodetector, rotating the photoreceptor web, and controlling the light source to emit light corresponding to line image data when it is the stored correct time corresponding to the count value of the pulse signal with respect to a light receiving termination point of the pulse signal.